There are needs for a data transmission system for transmitting a stream such as a TS by radio. The needs include, for example, a system for transmitting a TS output from an encoder in a data recording-reproducing apparatus through a wireless network (including a wireless sending device and a wireless receiving device) to a television (TV) set with a built-in digital tuner. In such data transmission system, the wireless sending device converts the TS, which is sent through a wired network (e.g., a network conforming to the IEEE1394 standard) from an encoder in the data recording-reproducing apparatus, into packets, and sends the packets through a wireless network to the wireless receiving device. The wireless receiving device reconstructs the received TS packets and sends them through a wired network (e.g., a network conforming to the IEEE1394 standard) to a TV with a built-in digital tuner. A decoder in the TV with a built-in digital tuner decodes the received TS.
Further, in such data transmission system, a PCR (program clock reference) is inserted into the TS in order to synchronize a clock in the sending-side encoder and a clock in the receiving-side decoder. The PCR is information used for adjusting a value of the STC (system time clock), which is a reference of time in the receiving-side decoder, to a value intended by the sending side. Accordingly, a timing when the PCR is input to the receiving-side decoder must be a timing intended by the sending side. In a TS, a TS packet including a PCR must be transmitted at least once in 100 ms. Therefore, the jitter in a TS including a PCR must be suppressed to several tens of microseconds (e.g., 50 μs) or less.
FIGS. 33A to 33C are diagrams for describing the conventional data transmission method. In FIG. 33A, timings, in which packets TS_0 to TS_17 are input to a wireless sending device, are shown, and TS's including the PCR (i.e., TS_0, TS_5, and TS_13) are marked with arrows. Further, in FIG. 33B, timings, in which the TS packets (packets TS_0 to TS_10 are shown) are transmitted from the wireless sending device to the wireless receiving device, are shown. Furthermore, in FIG. 33C, timings, in which the received TS's (TS_0 to TS_7 are shown) are output from the wireless receiving device, are shown. As shown in FIGS. 33A to 33C, the wireless receiving device outputs the TS's received from the wireless sending device with a predetermined amount of data delay. The amount of the jitter of the delayed received TS must be kept within a predetermined range, and, for this reason, the ATM (Asynchronous Transfer Mode) is used, for example (refer to Patent Documents 1 to 4, for example).
Patent Documents 1 to 4 describe a communication method using an SRTS (Synchronous Residual Time Stamp) method and another communication method using an adaptive clock method. The SRTS method is used when a common clock of the sending side and the receiving side can be referenced. The sending side measures the common clock at intervals of fixed data transfer rate information for every N bits, inserts just a portion of the measured value varied with fluctuation in the transmission clock frequency as synchronous residual time stamp information into the packet, and sends the packet. The receiving side reproduces the intervals of N-bit fixed rate information from the sent synchronous residual time stamp information and the common clock, and regenerates the clock in accordance with the intervals. On the other hand, in the adaptive clock method, the receiving side stores the fixed rate information included in the received packet in a buffer, and the read clock information of the buffer is controlled so that an amount of the stored information can be kept at a reference value.
Patent Document 1: Japanese Patent-Application Kokai (Laid Open) Publication No. H9-214477
Patent Document 2: Japanese Patent Application Kokai (Laid Open) Publication No. H7-46257
Patent Document 3: Japanese Patent Application Kokai (Laid Open) Publication No. H9-36846
Patent Document 4: Japanese Patent Application Kokai (Laid Open) Publication No. H5-210914
Patent Document 5: Japanese Patent Application Kokai (Laid Open) Publication No. H11-317768 (FIG. 1 and FIG. 2)